CN103917907B - Imaging lens system and camera head - Google Patents
Imaging lens system and camera head Download PDFInfo
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- CN103917907B CN103917907B CN201280054449.5A CN201280054449A CN103917907B CN 103917907 B CN103917907 B CN 103917907B CN 201280054449 A CN201280054449 A CN 201280054449A CN 103917907 B CN103917907 B CN 103917907B
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B13/00—Optical objectives specially designed for the purposes specified below
- G02B13/001—Miniaturised objectives for electronic devices, e.g. portable telephones, webcams, PDAs, small digital cameras
- G02B13/0015—Miniaturised objectives for electronic devices, e.g. portable telephones, webcams, PDAs, small digital cameras characterised by the lens design
- G02B13/002—Miniaturised objectives for electronic devices, e.g. portable telephones, webcams, PDAs, small digital cameras characterised by the lens design having at least one aspherical surface
- G02B13/0045—Miniaturised objectives for electronic devices, e.g. portable telephones, webcams, PDAs, small digital cameras characterised by the lens design having at least one aspherical surface having five or more lenses
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B13/00—Optical objectives specially designed for the purposes specified below
- G02B13/04—Reversed telephoto objectives
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B13/00—Optical objectives specially designed for the purposes specified below
- G02B13/18—Optical objectives specially designed for the purposes specified below with lenses having one or more non-spherical faces, e.g. for reducing geometrical aberration
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B9/00—Optical objectives characterised both by the number of the components and their arrangements according to their sign, i.e. + or -
- G02B9/04—Optical objectives characterised both by the number of the components and their arrangements according to their sign, i.e. + or - having two components only
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B9/00—Optical objectives characterised both by the number of the components and their arrangements according to their sign, i.e. + or -
- G02B9/34—Optical objectives characterised both by the number of the components and their arrangements according to their sign, i.e. + or - having four components only
- G02B9/58—Optical objectives characterised both by the number of the components and their arrangements according to their sign, i.e. + or - having four components only arranged - + + -
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Abstract
The invention provides a kind of Wide-angle and small-sized imaging lens system. disposing successively the 1st set of lenses (G1), diaphragm (St) from thing side and have the imaging lens system that the 2nd set of lenses (G2) of positive focal power forms, the 1st set of lenses (G1) dispose there are the 1st lens (L1) of negative focal power, the 2nd lens (L2) with positive focal power form. and the focal length of working as lens combination entirety is made as f, the focal length of the 1st set of lenses (G1) is made as fl, the distance on optical axis of the thing side lens face of the picture side lens face of the 1st lens (L1) and the 2nd lens (L2) is made as d12, lens face to the distance on optical axis of imaging surface (Sim) of the most close thing side of the 1st set of lenses (G1) when infinity object is focused is made as TL, when maximum image height is made as Y, meet following conditional (1)～(3),-0.50 < f/fl < 0.20... (1), 0.08 < d12/f < 0.35... (2), 2.5 < TL/Y < 4.0... (3).
Description
Technical Field
The present invention relates to an imaging lens, and more particularly to a small wide-angle lens suitable for an imaging device such as an electronic camera.
The present invention also relates to an imaging device including such an imaging lens.
Background
In recent years, a large number of digital cameras equipped with large-sized image pickup elements conforming to, for example, the APS (advanced photographic system) format, the 4/3 format, and the like have been commercially available. Recently, there have been proposed a lens-interchangeable digital camera and a compact camera using the large-sized image pickup device and having no reflex viewfinder, not limited to the digital single-lens reflex camera. These cameras have advantages of high image quality, small size of the entire system, and excellent portability. In addition, the demand for a small lens system is particularly increasing. As the wide-angle lens corresponding to such a large-sized image pickup device, for example, wide-angle lenses shown in patent documents 1 to 4 can be cited.
Conventionally, as a wide-angle lens to be mounted in a digital camera or a video camera, a negative focal length type lens is known which is composed of a front group having negative refractive power and a rear group having positive refractive power. In wide-angle lenses mounted in digital cameras and the like, it is necessary to secure a wide angle of view and to have a back focus into which various filters and optical members can be inserted, and therefore, the negative focus type lens that can obtain a long back focus with respect to a focal length is widely used. Typical examples thereof are shown in patent documents 1 and 2. Patent document 3 discloses an example of an imaging lens having a compact configuration with a small number of lenses.
In the interchangeable lens of the single-lens reflex camera, in order to secure a wide angle of view and obtain a long back focus, there is a case where the lens must be of a negative focus type, but when such a long back focus is not required, or when miniaturization and thinning are prioritized, a configuration in which the negative magnification is reduced may be appropriately adopted in the wide-angle lens. In this case, a so-called telescopic structure composed of a front group having positive refractive power and a rear group having negative refractive power, which is opposite to the negative focal length type magnification arrangement, or another type of structure may be adopted.
In the telephoto type, the overall length of the lens is easily shortened, but when the positive lens group is located forward, the incident angle (angle with respect to the optical axis) of the off-axis principal ray incident on the subsequent group becomes large, and therefore, there is a problem that it is difficult to correct aberration when a wide angle is realized. In contrast, it is also considered to adopt a compromise type of these two types, specifically, for example, a structure in which a negative lens is used for a lens closest to the object side and the front group as a whole has a positive power is considered. For example, patent document 4 discloses an example of an imaging lens having a configuration in which the negative lens is located forward but the entire front group has positive optical power. As the above-described compromise type structure, a structure in which a simple wide conversion lens portion is provided on the object side of the telephoto type lens may be considered.
[ Prior Art document ]
[ patent document ]
Patent document 1: japanese laid-open patent publication No. 6-160706
Patent document 2: japanese patent laid-open No. 2008-40033
Patent document 3: japanese patent laid-open publication No. 2011-
Patent document 4: japanese laid-open patent publication No. 2009-258157
Disclosure of Invention
[ problem to be solved by the invention ]
The negative focal length type imaging lenses disclosed in patent documents 1 and 2 recognize a problem that the overall length is inevitably large. Further, this type of imaging lens is also characterized in that the front group has a large air space, and the diameter of the 1 st lens also tends to increase. In addition, in this type of imaging lens, it is difficult to correct aberrations because the lens groups in front of and behind the aperture stop lack symmetry, and if a sufficiently wide angle and a sufficiently large diameter are achieved, the number of lenses increases and the size increases inevitably. As an example of an imaging lens having a small number of lenses and a compact configuration, an imaging lens shown in patent document 3 is exemplified as described above, and a sufficiently wide angle of view cannot be obtained when the angle of view of the imaging lens shown here is 61 °.
On the other hand, the image pickup lens disclosed in the above-mentioned trade-off type patent document 4 can be configured to be compact with a small number of lenses, but cannot obtain a sufficiently wide angle of view even when the angle of view is 62 °.
The present invention has been made in view of the above problems, and an object thereof is to provide an imaging lens that can be formed in a small size and can secure a wide angle of view.
The present invention also provides an imaging device that includes the above-described imaging lens, can be formed in a compact size, and can take a picture at a wide angle of view.
[ MEANS FOR solving PROBLEMS ] A method for solving the problems
The image pickup lens of the present invention is characterized in that,
substantially comprises a 1 st lens group having negative or positive refractive power, a stop, and a 2 nd lens group having positive refractive power arranged in this order from the object side,
the 1 st lens group is substantially composed of three or less lenses as a whole, in which a 11 th lens group having negative refractive power and a 12 th lens group having positive refractive power are arranged in this order from the object side,
the 11 th lens group is composed of one 1 st lens, the 12 th lens group is composed of a positive lens component which is a single lens or a cemented lens arranged with an air gap from the 1 st lens,
the 2 nd lens group is substantially composed of a 21 st lens group having positive refractive power and a 22 nd lens group having negative refractive power arranged in this order from the object side,
the 21 st lens group has at least one positive lens and at least one negative lens,
the 22 nd lens group is substantially composed of a total of three lenses including at least one positive lens and at least one negative lens,
when the focal length of the entire lens system is f, the focal length of the 1 st lens group is f1, the axial distance between the image-side lens surface of the 1 st lens in the 1 st lens group and the lens surface of the positive lens component closest to the object side is d12, the axial distance from the lens surface of the 1 st lens group closest to the object side to the image forming surface in infinity object focusing (back focal length is air converted length) is TL, and the maximum image height is Y, the following conditional expressions are satisfied,
-0.50＜f/f1＜0.20...(1)
0.08＜d12/f＜0.35...(2)
2.5＜TL/Y＜4.0...(3)。
the phrase "substantially composed of …" recited in the three places above means that the phrase includes not only the lens group as a constituent element exemplified herein but also a case where the phrase includes substantially a mechanism portion such as an optical element, a lens flange, a lens barrel, an imaging element, and a camera-shake correction mechanism, etc., other than a lens having no magnification, a stop, a cover glass, etc.
In addition, the sign of the surface shape and the refractive power of the lens of the imaging lens of the present invention is considered in the paraxial region for a lens including an aspherical surface.
In addition, the imaging lens of the present invention preferably satisfies at least one of the following conditional expressions in particular within the ranges defined by the conditional expressions (1) to (3),
-0.45＜f/f1＜0.15...(1’)
0.10＜d12/f＜0.32...(2’)
2.7＜TL/Y＜3.8...(3’)。
in addition, within the range defined by the above conditional expression (1) or (1'), it is preferable that the following conditional expression is also satisfied,
-0.42＜f/f1＜0.10...(1”)。
preferably, the 22 nd lens group is composed of only a sub-lens group having negative refractive power and one positive lens, which are arranged in order from the object side.
In the imaging lens of the present invention, it is preferable that the average value of the refractive indexes with respect to the d-line of all the lenses arranged in the 22 Nd lens group is Nd22, and that the following conditional expression is satisfied,
1.75＜Nd22...(4)。
in addition, the imaging lens of the present invention preferably satisfies, in particular, the following conditional expression within the range defined by the conditional expression (4),
1.78＜Nd22...(4’)。
in addition, it is preferable that a lens having an aspherical surface on at least one surface is disposed in the 22 nd lens group.
In the 22 nd lens group, a negative lens is preferably disposed in which a lens surface on the object side of the paraxial region is concave with respect to the object side and at least one surface is aspheric.
On the other hand, the 21 st lens group is preferably composed of three lenses in total, namely, two lenses and one positive lens, which are joined to each other with one positive lens and the other negative lens.
In addition, a positive lens having at least one aspherical surface is preferably disposed in the 21 st lens group.
In the imaging lens of the present invention, it is preferable that in an infinity object focus state, when an axial distance from a lens surface closest to the object side in the 1 st lens group to a lens surface closest to the image side in the 2 nd lens group is Σ d and an axial distance from a lens surface closest to the object side in the 1 st lens group to an image forming surface (back focal length is an air conversion length) is TL, the following conditional expression is satisfied,
1.1＜TL/∑d＜1.5...(5)。
in addition, the imaging lens of the present invention preferably satisfies, in particular, the following conditional expression within the range defined by the conditional expression (5),
1.20＜TL/∑d＜1.45...(5’)。
in the imaging lens of the present invention, when the focal length of the 1 st lens is f1n and the focal length of the entire system is f, the following conditional expression is preferably satisfied,
0.8＜|f1n|/f＜1.2...(6)。
in addition, the imaging lens of the present invention preferably satisfies the following conditional expression, in particular, within the range defined by the conditional expression (6),
0.82＜|f1n|/f＜1.15...(6’)。
in the imaging lens of the present invention, it is preferable that when a curvature radius of the image side lens surface of the 1 st lens element is R12 and a curvature radius of the lens surface closest to the object side of the positive lens component is R21, the following conditional expression is satisfied,
2.0＜(R21+R12)/(R21-R12)＜4.0...(7)。
in addition, the imaging lens of the present invention preferably satisfies, in particular, the following conditional expression within the range defined by the conditional expression (7),
2.2＜(R21+R12)/(R21-R12)＜3.8...(7’)。
preferably, the 22 nd lens group includes three lenses, i.e., a negative lens, and a positive lens, which are arranged in this order from the object side.
Preferably, the 12 th lens group is composed of only one positive lens.
On the other hand, the imaging device of the present invention is characterized by including the imaging lens of the present invention described above.
[ Effect of the invention ]
As described above, the imaging lens of the present invention is configured by arranging, in order from the object side, the 1 st lens group having negative or positive power, the stop, and the 2 nd lens group having positive power. The 1 st lens group includes, in order from the object side, an 11 th lens group having negative refractive power and including one 1 st lens, and a 12 th lens group including a positive lens component, which is a single lens or a cemented lens, and which is disposed at an air interval from the 1 st lens. That is, since the focal length of the entire 1 st lens group is longer and the magnification is weaker than the focal length of the entire optical system, it can be considered that a simple wide-angle conversion lens is configured to shorten the focal length of the entire lens system. On the other hand, the 2 nd lens group is composed entirely of a 21 st lens group having positive power and a 22 nd lens group having negative power.
That is, the imaging lens of the present invention is configured such that the 1 st lens group, which is a simple wide-angle conversion lens, is added to the 2 nd lens group, which is regarded as a main lens unit and includes a front group having positive refractive power and a rear group having negative refractive power, and is arranged with a telescopic magnification.
The negative lens group is preferably moved forward to achieve a wide angle, but if the negative focal length type is adopted, the overall length of the lens becomes large, whereas if the positive lens group is moved forward, the thickness can be easily reduced, but it becomes very difficult to correct off-axis aberrations to achieve a wide angle. In the imaging lens according to the present invention, the above-described structure of the compromise type, that is, the structure in which the simple wide-angle converting portion that does not become too thick is provided on the object side of the telephoto type main lens portion is considered, and therefore, downsizing and widening can be achieved at the same time.
Alternatively, the imaging lens of the present invention does not require a long back focus as a single-lens reflex interchangeable lens, but can be said to have a lens structure in which the power arrangement is optimized for a back focus that is necessary and sufficient in an imaging device that requires a somewhat long back focus.
Next, effects obtained by satisfying the conditional expressions (1) to (3) will be described. The conditional expression (1) is a condition for correcting each aberration favorably by setting the 1 st lens group to a weak divergent system or a weak convergent system. That is, when the positive power is stronger beyond the upper limit value, it becomes difficult to correct coma aberration or to secure a desired back focal length. Conversely, when the negative power becomes stronger below the lower limit value, distortion aberration occurs due to the divergence. In order to suppress this phenomenon, correction of field curvature becomes difficult. When the conditional expression (1) is satisfied, the above-described problems can be prevented, and each aberration can be corrected satisfactorily.
Conditional expression (2) defines the relationship between the air space between the 1 st lens, which is a negative lens, disposed in the 1 st lens group and the positive lens component disposed closer to the image side than the air space and the focal length of the entire lens system, and if the air space is higher than the upper limit value, spherical aberration and coma aberration are favorably corrected, but the 1 st lens group is not preferable because the entire lens system becomes thick. Conversely, if the value is lower than the lower limit value, correction of the above aberrations is not facilitated, and the intensity of ghost light due to reflection at the image side lens surface of the 1 st lens element and the object side lens surface of the positive lens component becomes strong, which is not preferable. When the conditional expression (2) is satisfied, the above-described problems can be prevented, and each aberration can be corrected satisfactorily.
Conditional expression (3) defines the relationship between the entire optical length and the maximum image height, and if it is higher than the upper limit value, it is advantageous in aberration correction, but the entire lens system becomes large, and is not preferable in terms of downsizing. Conversely, if the value is lower than the lower limit value, it is difficult to correct spherical aberration and field curvature of the entire lens system, which is not preferable. When the conditional expression (3) is satisfied, the above-described problems can be prevented, the aberrations can be corrected favorably, and the reduction in size can be achieved.
The effects of the conditional expressions (1) to (3) described above are more remarkable when at least one of the conditional expressions (1 ') to (3') is satisfied even within the range defined by the conditional expressions. In particular, when the conditional expression (1 ") is also satisfied, each aberration can be corrected more favorably.
In the imaging lens of the present invention, particularly in the case where the 22 nd lens group is composed of only a sub-lens group having negative refractive power and one positive lens, which are arranged in order from the object side, the positive lens can suppress an incident angle of the off-axis light to the imaging element.
In the imaging lens of the present invention, the following effects can be obtained particularly when the conditional expression (4) is satisfied. That is, the conditional expression (4) defines an average value of refractive indexes of all the lenses arranged in the 22 nd lens group, and is not preferable because if the average value is lower than a lower limit value thereof, control of the petzval sum is difficult, and correction of field curvature is difficult. When the conditional expression (4) is satisfied, the above-described problems can be prevented, and the field curvature can be corrected satisfactorily.
The above-described effect is more remarkable in the case where the conditional expression (4') is satisfied within the range defined by the conditional expression (4).
In the imaging lens of the present invention, particularly in the case where a lens having at least one aspherical surface is disposed in the 22 nd lens group, the entire imaging lens can be made thin and the balance between spherical aberration and field curvature can be easily controlled.
In particular, in the case of a negative lens in which the paraxial region is disposed in the 22 nd lens group, the lens surface on the object side is concave with respect to the object side, and at least one surface is aspheric, a large aberration correction effect can be obtained by providing an aspheric surface to the negative lens that inevitably causes a large change in the angle of light rays incident thereto due to downsizing.
In addition, when the 21 st lens group is composed of three lenses in total, i.e., two lenses in which one lens is a positive lens and the other lens is a negative lens, and one positive lens, chromatic aberration can be corrected satisfactorily by the action of the cemented lenses. Also in this case, correction of spherical aberration is facilitated by providing a positive lens in the 21 st lens group disposed immediately after the stop.
In the case where the 21 st lens group is formed by the three lenses, it is more preferable that a negative lens, a positive lens joined to the negative lens, and a positive lens are arranged in this order from the object side, and the negative lens is arranged closest to the object side, so that the petzval sum can be easily suppressed. When such a configuration is provided, although correction of spherical aberration is slightly disadvantageous, correction of spherical aberration can be favorably performed by providing another positive single lens in addition to the two joined lenses.
In addition, when a positive lens having an aspherical surface on at least one surface is disposed in the 21 st lens group, the effect of correcting spherical aberration and coma aberration can be further improved.
In the imaging lens of the present invention, the following effects can be obtained particularly when the conditional expression (5) is satisfied. That is, the conditional expression (5) defines the relationship between the distance on the optical axis from the lens surface closest to the object side in the 1 st lens group to the lens surface closest to the image side in the 2 nd lens group and the distance on the optical axis from the lens surface closest to the object side in the 1 st lens group to the image forming surface, and if it is higher than the upper limit value thereof, the entire lens system becomes large, and it is difficult to achieve both downsizing and high performance. Conversely, if the value is lower than the lower limit value, it is difficult to correct spherical aberration and field curvature in a well-balanced manner, and it is difficult to secure a desired back focus. When the conditional expression (5) is satisfied, the above-described problems can be prevented, both downsizing and high performance can be achieved, spherical aberration and field curvature can be corrected in a well-balanced manner, and a desired back focus can be easily secured.
The above-described effect is more remarkable in the case where the conditional expression (5') is satisfied within the range defined by the conditional expression (5).
In the imaging lens of the present invention, the following effects can be obtained particularly when the conditional expression (6) is satisfied. That is, the conditional expression (6) defines the relationship between the focal length of the 1 st lens and the focal length of the entire system, and if the relationship is lower than the lower limit value and the negative magnification of the 1 st lens group becomes strong, the field curvature and the petzval sum increase in the negative direction. Conversely, when the value is higher than the upper limit value, it is difficult to correct coma aberration, and it is difficult to secure a desired back focus. When conditional expression (6) is satisfied, the above-described problems can be prevented, the field curvature and the petzval sum can be suppressed to be small, coma can be corrected well, and a desired back focus can be easily secured.
The above-described effect is more remarkable in the case where the conditional expression (6') is satisfied within the range defined by the conditional expression (6).
In the imaging lens of the present invention, the following effects can be obtained particularly when the conditional expression (7) is satisfied. That is, the conditional expression (7) defines the relationship between the radius of curvature of the image-side lens surface of the 1 st lens and the radius of curvature of the lens surface closest to the object side of the positive lens component disposed with an air gap from the 1 st lens L1, and is not preferable because the distortion aberration and the field curvature become large when the relationship is higher than the upper limit value. Conversely, when the value is lower than the lower limit value, correction of coma aberration is difficult, and therefore, this is not preferable. When conditional expression (7) is satisfied, the above-described problems can be prevented, distortion aberration and field curvature can be suppressed to a small degree, and coma can be easily corrected.
The above-described effect is more remarkable in the case where the conditional expression (7') is satisfied within the range defined by the conditional expression (7).
In the imaging lens of the present invention, particularly in the case where the 22 nd lens group is formed of three lenses, i.e., a negative lens, and a positive lens, which are arranged in this order from the object side, it is advantageous in terms of downsizing.
In the imaging lens of the present invention, particularly in the case where the 12 th lens group is formed by only one positive lens, it is particularly advantageous in terms of downsizing.
On the other hand, since the image pickup device of the present invention includes the image pickup lens of the present invention which achieves the above-described effects, it is possible to perform image pickup with a wide angle of view and also achieve reduction in size and weight.
Drawings
Fig. 1 is a cross-sectional view showing a lens structure of an imaging lens according to embodiment 1 of the present invention.
Fig. 2 is a cross-sectional view showing a lens structure of an imaging lens according to embodiment 2 of the present invention.
Fig. 3 is a cross-sectional view showing a lens structure of an imaging lens according to embodiment 3 of the present invention.
Fig. 4 is a cross-sectional view showing a lens structure of an imaging lens according to example 4 of the present invention.
Fig. 5 is a cross-sectional view showing a lens structure of an imaging lens according to example 5 of the present invention.
Fig. 6 is a cross-sectional view showing a lens structure of an imaging lens according to example 6 of the present invention.
Fig. 7 is a cross-sectional view showing a lens structure of an imaging lens according to example 7 of the present invention.
Fig. 8 is a cross-sectional view showing a lens structure of an imaging lens according to example 8 of the present invention.
Fig. 9 is a cross-sectional view showing a lens structure of an imaging lens according to example 9 of the present invention.
Fig. 10(a) to (D) are aberration diagrams showing the imaging lens according to example 1 of the present invention.
Fig. 11(a) to (D) are aberration diagrams showing the imaging lens according to example 2 of the present invention.
Fig. 12(a) to (D) are aberration diagrams showing the imaging lens according to example 3 of the present invention.
Fig. 13(a) to (D) are aberration diagrams showing the imaging lens according to example 4 of the present invention.
Fig. 14(a) to (D) are aberration diagrams showing the imaging lens according to example 5 of the present invention.
Fig. 15(a) to (D) are aberration diagrams showing the imaging lens according to example 6 of the present invention.
Fig. 16(a) to (D) are aberration diagrams showing the imaging lens according to example 7 of the present invention.
Fig. 17(a) to (D) are aberration diagrams showing the imaging lens according to example 8 of the present invention.
Fig. 18(a) to (D) are aberration diagrams showing the imaging lens according to example 9 of the present invention.
Fig. 19 is a schematic configuration diagram of an imaging apparatus according to an embodiment of the present invention.
Fig. 20A is a schematic front view of an image pickup apparatus according to another embodiment of the present invention.
Fig. 20B is a schematic back view of the image pickup apparatus shown in fig. 20A.
Detailed Description
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Fig. 1 is a cross-sectional view showing a configuration example of an imaging lens according to an embodiment of the present invention, and corresponds to an imaging lens of example 1 described later. Fig. 2 to 9 are cross-sectional views showing other configuration examples according to the embodiment of the present invention, and correspond to the imaging lenses of examples 2 to 9 described later. The basic configuration of the example shown in fig. 1 to 9 is the same as that of the example shown in fig. 9 except that only the 1 st lens group G1 is composed of three lenses, and the same method is shown, and therefore the imaging lens according to the embodiment of the present invention will be described here mainly with reference to fig. 1.
Fig. 1 shows an optical system configuration in an infinity-focused state with the left side as the object side and the right side as the image side. This is also the same in fig. 2 to 9 described later.
In the imaging lens of the present embodiment, a 1 st lens group G1 having negative or positive refractive power and a 2 nd lens group G2 having positive refractive power are arranged in this order from the object side as lens groups. An aperture stop St is disposed between the 1 St lens group G1 and the 2 nd lens group G2.
The 1 st lens group G1 includes, in order from the object, an 11 th lens group G11 having negative refractive power and a 12 th lens group G12 having positive refractive power. The 1 st lens group G1 is composed of three or less lenses as a whole, and in the present embodiment, the 11 th lens group G11 is composed of one 1 st lens L1 which is a negative lens (a lens having negative refractive power), and the 12 th lens group G12 is composed of one 2 nd lens L2 which is a positive lens (a lens having positive refractive power).
In examples 2 to 8 to be described later, the 12 th lens group G12 has the same structure. In contrast, in example 9, the 12 th lens group G12 is composed of a positive lens L2a and a negative lens L2b joined to each other. The cemented lens constituted by the lenses L2a and L2b is a lens having positive refractive power. In the present invention, such a cemented lens and the 2 nd lens L2 as a single lens having a positive refractive power as well are collectively referred to as a "positive lens component".
On the other hand, the 2 nd lens group G2 includes, in order from the object side, a 21 st lens group G21 having positive refractive power and a 22 nd lens group G22 having negative refractive power. Each of the 21 st lens group G21 and the 22 nd lens group G22 includes at least one positive lens and at least one negative lens. In the present embodiment, the 21 st lens group G21 includes, in order from the object side, a 3 rd lens L3 which is a negative lens, a 4 th lens L4 which is a positive lens joined to the 3 rd lens L3, and a 5 th lens L5 which is a positive lens. On the other hand, the 22 nd lens group G22 is provided with, in order from the object side, a 6 th lens L6 which is a negative lens, a 7 th lens L7 which is also a negative lens, and an 8 th lens L8 which is a positive lens.
The aperture stop St shown in fig. 1 does not necessarily indicate the size or shape, but indicates the position on the optical axis Z. Here, Sim is an image plane, and an imaging element, for example, a ccd (charge coupled device), a cmos (complementary metal oxide semiconductor), or the like is arranged at this position as described later.
Fig. 1 also shows an example in which a parallel flat plate-shaped optical member PP is disposed between the 2 nd lens group G2 and the image formation surface Sim. When the imaging lens is applied to an imaging device, various filters such as a glass cover, an infrared cut filter, and a low pass filter are often disposed between the optical system and the image plane Sim depending on the configuration of the imaging device side where the lens is mounted. The optical member PP is obtained by assuming these. In recent image pickup apparatuses, a 3CCD system using CCDs for each color is adopted to achieve high image quality, and a color separation optical system such as a color separation prism is interposed between a lens system and an image forming surface Sim to cope with the 3CCD system. Such a color separation optical system can be arranged as the optical member PP.
In the imaging lens of the present embodiment, focusing is achieved by moving the entire optical system along the optical axis Z.
Hereinafter, the lenses constituting each lens group will be described in detail. For example, the 1 st lens element L1 is a biconcave lens element, the 2 nd lens element L2 is a planoconvex lens element having a convex surface facing the object side (left side in fig. 1), the 3 rd lens element L3 is a negative meniscus lens element having a concave surface facing the image side (i.e., the image plane Sim side and the right side in fig. 1), the 4 th lens element L4 is a biconvex lens element, the 5 th lens element L5 is a biconvex lens element, the 6 th lens element L6 is a planoconcave lens element having a concave surface facing the image side, the 7 th lens element L7 is a negative meniscus lens element having a concave surface facing the object side, and the 8 th lens element L8.
The imaging lens of the present embodiment is configured such that a 1 st lens group G1, which is a simple wide-angle conversion lens, is added to a 2 nd lens group G2, which is a main lens unit and is arranged with a telescopic magnification, and which includes a front group (21 st lens group G21) having positive power and a rear group (22 nd lens group G22) having negative power. The imaging lens can realize miniaturization and wide angle at the same time.
In the present imaging lens, assuming that the focal length of the entire lens system is f, the focal length of the 1 st lens group G1 is f1, the axial distance between the image side lens surface of the 1 st lens L1 in the 1 st lens group G1 and the lens surface closest to the object side of the 2 nd lens L2 which is the positive lens component is d12, the axial distance (air converted length is used as the back focal length) from the lens surface closest to the object side in the 1 st lens group G1, i.e., the object side lens surface of the 1 st lens L1 to the image forming surface Sim in infinity object focusing is TL, and the maximum image height is Y, the following conditional expressions are satisfied,
-0.50＜f/f1＜0.20...(1)
0.08＜d12/f＜0.35...(2)
2.5＜TL/Y＜4.0...(3)。
in addition, within the ranges defined by the conditional expressions (1) to (3), the following conditional expressions are satisfied,
-0.45＜f/f1＜0.15...(1’)
0.10＜d12/f＜0.32...(2’)
2.7＜TL/Y＜3.8...(3’)。
in addition, within the range defined by the conditional expression (1) or (1'), the following conditional expression is satisfied
-0.42＜f/f1＜0.10...(1”)。
Table 19 summarizes and describes specific values of the conditional expressions (1) to (3), i.e., the literal expressions, for each example. This is also the case with conditional expressions (4) to (7) described later.
As described above, the imaging lens of the present embodiment achieves the following effects by satisfying all of the conditional expressions (1) to (3). That is, conditional expression (1) is a condition for correcting each aberration well by setting the 1 st lens group G1 to a weak divergent system or a weak convergent system, and when the positive magnification is stronger beyond the upper limit value, correction of coma aberration becomes difficult or it becomes difficult to secure a desired back focal length. Conversely, when the negative power becomes stronger below the lower limit value, distortion aberration occurs due to its divergence. However, in order to suppress this phenomenon, correction of field curvature becomes difficult. When the conditional expression (1) is satisfied, the above-described problems can be prevented, and each aberration can be corrected satisfactorily.
Conditional expression (2) is a conditional expression that defines a relationship between an air space between the 1 st lens L1 as a negative lens disposed in the 1 st lens group G1 and the 2 nd lens L2 as a positive lens component disposed on the image side thereof and a focal length of the entire lens system, and is higher than the upper limit thereof, although it is advantageous to correct spherical aberration and coma aberration, it is not preferable that the 1 st lens group G1 becomes thicker as a whole. Conversely, if the value is lower than the lower limit value, the correction of the above aberrations is not facilitated, and the intensity of ghost light due to reflection at the image side lens surface of the 1 st lens L1 and the object side lens surface of the 2 nd lens L2 becomes strong, which is not preferable. When the conditional expression (2) is satisfied, the above-described problems can be prevented, and each aberration can be corrected satisfactorily.
The conditional expression (3) defines the relationship between the entire optical length and the maximum image height, and if it is higher than the upper limit value, it is advantageous in aberration correction, but the entire lens system becomes large, which is not preferable in terms of downsizing. Conversely, if the value is lower than the lower limit value, it is difficult to correct spherical aberration and field curvature of the entire lens system, which is not preferable. When the conditional expression (3) is satisfied, the above-described problems can be prevented, each aberration can be corrected favorably, and further, downsizing can be achieved.
In the imaging lens according to the present embodiment, the above-described effects are more remarkable because all of the conditional expressions (1 ') to (3') are satisfied, and the conditional expression (1 ") is satisfied, within the ranges defined by the conditional expressions (1) to (3). It is not necessary that all of the conditional expressions (1 ') to (3') are satisfied, and the above-described advantageous effects can be obtained by satisfying one of the conditional expressions.
In the imaging lens of the present embodiment, the 22 nd lens group G22 is composed of only a sub-lens group (composed of the 6 th lens L6 and the 7 th lens L7) having negative refractive power and one 8 th lens L8 which is a positive lens, which are arranged in this order from the object side. In this configuration, the incident angle of the off-axis light to the image pickup element can be suppressed to be small by the 8 th lens L8 which is a positive lens.
In the imaging lens of the present embodiment, when the average refractive index of all the lenses arranged in the 22 Nd lens group G22, i.e., the 6 th lens L6, the 7 th lens L7, and the 8 th lens L8 with respect to the d-line is Nd22, the following conditional expression is satisfied,
1.75＜Nd22...(4)
in addition, the following conditional expression (see Table 19) is satisfied within the range specified by the conditional expression (4),
1.78＜Nd22...(4’)。
by satisfying the conditional expression (4), the imaging lens of the present embodiment achieves the following effects. That is, the conditional expression (4) is a conditional expression which defines an average value of refractive indexes of all the lenses arranged in the 22 nd lens group G22, and if the average value is lower than a lower limit value thereof, control of Petzval sum becomes difficult, and correction of field curvature becomes difficult, which is not preferable. When the conditional expression (4) is satisfied, the above-described problems can be prevented, and the field curvature can be corrected satisfactorily.
In the imaging lens of the present embodiment, the above-described effect is more remarkable because the conditional expression (4') is satisfied even within the range specified by the conditional expression (4).
In the imaging lens of the present embodiment, the 7 th lens L7 having aspherical lens surfaces on the object side and the image side is disposed in the 22 nd lens group G22. By disposing the 7 th lens L7 in the 22 nd lens group G22, the entire imaging lens can be made thin, and the balance between spherical aberration and field curvature can be easily controlled.
More specifically, in the 7 th lens L7, the object side lens surface is concave with respect to the object side in the paraxial region, and both the object side and image side lens surfaces are aspheric negative lenses. In order to achieve downsizing, the angle of the light beam incident on the 7 th lens L7 is inevitably changed greatly, but a large aberration correction effect can be obtained by forming the 7 th lens L7 into the above shape.
In the imaging lens of the present embodiment, the 21 st lens group G21 is composed of three lenses in total of two lenses (the 3 rd lens L3 and the 4 th lens L4) in which one lens is a positive lens and the other lens is a negative lens and which are joined to each other, and one positive lens (the 5 th lens L5). In this configuration, chromatic aberration can be corrected satisfactorily by the action of the cemented lens composed of the 3 rd lens L3 and the 4 th lens L4. Also in this case, correction of spherical aberration is facilitated by providing a positive lens in the 21 st lens group G21 disposed immediately after the stop.
The three lenses are arranged in order from the object side as a negative lens (the 3 rd lens L3), a positive lens (the 4 th lens L4) joined to the negative lens, and a positive lens (the 5 th lens L5). By disposing the negative lens closest to the object side in this manner, the petzval sum is easily suppressed. In addition, although the configuration described above is slightly disadvantageous in correcting spherical aberration, it is possible to satisfactorily correct spherical aberration by providing the 5 th lens L5, which is another positive single lens, in addition to the two lenses L3 and L4 that are joined.
In the imaging lens of the present embodiment, a 5 th lens L5 which is a positive lens having aspheric lens surfaces on both the object side and the image side is disposed in the 21 st lens group G21. By disposing the 5 th lens L5, the effect of correcting spherical aberration and coma aberration can be further improved.
In the imaging lens of the present embodiment, when the distance on the optical axis from the object side lens surface of the 1 st lens L1 to the image side lens surface of the 8 th lens L8 is Σ d and the distance on the optical axis from the object side lens surface of the 1 st lens L1 to the image forming surface Sim (the back focal length is an air conversion length) is TL in the infinity object focus state, the following conditional expression is satisfied,
1.1＜TL/∑d＜1.5...(5)
in addition, within the range defined by the conditional expression (5), the following conditional expression (see Table 19) is satisfied,
1.20＜TL/∑d＜1.45...(5’)。
by satisfying the conditional expression (5), the imaging lens of the present embodiment achieves the following effects. That is, the conditional expression (5) is a conditional expression that defines a relationship between an on-axis distance from the object-side-closest lens surface of the 1 st lens group G1 to the image-side-closest lens surface of the 2 nd lens group G2 and an on-axis distance from the object-side-closest lens surface of the 1 st lens group G1 to the image forming surface Sim, and if it is higher than the upper limit value thereof, the entire lens system becomes large, and it becomes difficult to achieve both downsizing and high performance. Conversely, if the value is lower than the lower limit value, it becomes difficult to correct spherical aberration and field curvature in a well-balanced manner, and it becomes difficult to secure a desired back focus. When the conditional expression (5) is satisfied, the above-described problems can be prevented, both downsizing and high performance can be achieved, spherical aberration and field curvature can be corrected in a well-balanced manner, and a desired back focus can be easily secured.
In the imaging lens according to the present embodiment, the above-described effect is more remarkable because the conditional expression (5') is satisfied even within the range defined by the conditional expression (5).
In the imaging lens of the present embodiment, when the focal length of the 1 st lens L1 is f1n and the focal length of the entire system is f, the following conditional expression is satisfied,
0.8＜|f1n|/f＜1.2...(6)
in addition, within the range defined by the conditional expression (6), the following conditional expression (see Table 19) is satisfied,
0.82＜|f1n|/f＜1.15...(6’)。
the imaging lens of the present embodiment achieves the following effects by satisfying the conditional expression (6). That is, conditional expression (6) is a conditional expression defining a relationship between the focal length of the 1 st lens L1 and the focal length of the entire system, and if the negative magnification of the 1 st lens group G1 is increased below the lower limit value thereof, the field curvature and the petzval sum increase in the negative direction. Conversely, if the value is higher than the upper limit value, it becomes difficult to correct coma aberration, and it becomes difficult to secure a desired back focus. When conditional expression (6) is satisfied, the above-described problems can be prevented, the field curvature and the petzval sum can be suppressed to be small, coma can be corrected well, and a desired back focus can be easily secured.
In the imaging lens according to the present embodiment, the above-described effect is more remarkable because the conditional expression (6') is satisfied even within the range defined by the conditional expression (6).
In the imaging lens of the present embodiment, when the curvature radius of the image side lens surface of the 1 st lens L1 is R12 and the curvature radius of the object side lens surface of the 2 nd lens L2, which is a positive lens component, is R21, the following conditional expression is satisfied,
2.0＜(R21+R12)/(R21-R12)＜4.0...(7)
in addition, within the range defined by the conditional expression (7), the following conditional expression (see Table 19) is satisfied,
2.2＜(R21+R12)/(R21-R12)＜3.8...(7’)。
by satisfying this conditional expression (7), the imaging lens of the present embodiment achieves the following effects. That is, the conditional expression (7) is a conditional expression defining a relationship between the radius of curvature of the image side lens surface of the 1 st lens L1 and the radius of curvature of the lens surface closest to the object side of the 2 nd lens L2 as a positive lens component disposed with an air space from the 1 st lens L1, and is not preferable because the distortion aberration and the field curvature become large when the conditional expression is higher than the upper limit value thereof. Conversely, when the value is lower than the lower limit value, correction of coma aberration is difficult, and therefore, this is not preferable. When conditional expression (7) is satisfied, the above-described problems can be prevented, distortion aberration and field curvature can be suppressed to a small degree, and coma can be easily corrected.
In the imaging lens according to the present embodiment, the above-described effect is more remarkable because the conditional expression (7') is satisfied even within the range defined by the conditional expression (7).
In the imaging lens of the present embodiment, the 22 nd lens group G22 includes three lenses, i.e., a 6 th lens L6 which is a negative lens, a 7 th lens L7 which is a negative lens, and an 8 th lens L8 which is a positive lens, which are arranged in this order from the object side. When the 22 nd lens group G22 is constituted by only three lenses in this way, it is particularly advantageous from the viewpoint of downsizing of the imaging lens.
In the imaging lens of the present embodiment, the 11 th lens group G11 is composed of only one 1 st lens L1 as a negative lens, and the 12 th lens group G12 is composed of only one 2 nd lens L2 as a positive lens. This structure is particularly advantageous in downsizing of the imaging lens.
Next, embodiments of the imaging lens of the present invention will be described in detail, particularly, numerical embodiments.
< example 1>
As described above, fig. 1 shows the arrangement of the lens groups of the image pickup lens of embodiment 1. Since the lens group and each lens in the configuration of fig. 1 are described in detail above, redundant description is omitted below unless otherwise necessary.
Table 1 shows basic lens data of the imaging lens of example 1. Here, the optical member PP is also included. In table 1, the column of Si shows the i-th (i 1, 2, 3, and..) surface number when the component is numbered so that the component closest to the object side has the surface number of the object side which is the 1 st and increases sequentially toward the image side. The column for Ri indicates the curvature radius of the ith surface, and the column for Di indicates the surface interval between the ith surface and the (i + 1) th surface on the optical axis Z. The column Ndj shows the refractive index of the jth (j 1, 2, 3, and..) component that increases sequentially toward the image side with the component closest to the object side being the 1 st component, and the column vdj shows the abbe number of the jth component with respect to the d-line (wavelength 587.6 nm). The basic lens data is also shown including the aperture stop St, and the column of the curvature radius of the surface corresponding to the aperture stop St is denoted by ∞ (aperture stop).
The values of the radius of curvature R and the surface interval D in table 1 are in mm. Table 1 shows the numerical values rounded to a predetermined number of digits. The sign of the curvature radius is positive when the surface shape is convex toward the object side and negative when the surface shape is convex toward the image side.
In the lens data in table 1, the aspheric surface is denoted by an x symbol, and the paraxial radius of curvature is shown as the radius of curvature of the aspheric surface. In addition, below table 1, the focal length f and fno of the entire lens system are shown.
The same applies to tables 3, 5, 7, 9, 11, 13, 15 and 17 described later.
Further, aspherical surface data of the image pickup lens of example 1 are shown in Table 2, where the surface number of the aspherical surface and the aspherical surface coefficient relating to the aspherical surface are shown, and where "E-n" (n: integer) of the numerical value of the aspherical surface coefficient is shown as "× 10-n". The aspherical surface coefficients are values of coefficients KA and Am (m is 3, 4, 5, and.. 16) in the following aspherical surface formula.
Zd＝C·h2/{1+(1-KA·C2·h2)1/2}+∑Am·hm
Wherein,
and (d) is as follows: aspheric depth (length of perpendicular drawn from a point on the aspheric surface having height h to the aspheric apex on a plane perpendicular to the optical axis)
h: height (distance from optical axis to lens surface)
C: reciprocal of paraxial radius of curvature
KA. Am, and (2): aspheric coefficients (m ═ 3, 4, 5,. 16)
The same applies to the methods described in table 2 described above in tables 4, 6, 8, 10, 12, 14, 16, and 18 described below.
In all tables described below, as described above, mm is used as a unit of length and degrees (°) is used as a unit of angle, but since an optical system can be used in a scaled-up or scaled-down manner, other appropriate units may be used.
[ TABLE 1 ]
Example 1 basic lens data
*: aspherical surface
f＝18.554FNo.＝2.06
[ TABLE 2 ]
Example 1. aspherical data
In table 19, values of the conditions defined by the conditional expressions (1) to (7), that is, values of the character expressions are shown in examples 1 to 9. The values of this table 19 are associated with the d-line. As shown here, the imaging lens of example 1 and the imaging lenses of examples 2 to 9 described later all satisfy conditional expressions (1) to (7), and further all satisfy conditional expressions (1 ') to (7') and (1 ") indicating more preferable ranges within the ranges defined by these conditional expressions. The effects obtained thereby are as described in detail above.
Fig. 10(a) to (D) show spherical aberration, astigmatism, distortion aberration (distortion), and chromatic aberration of magnification in the infinity focusing state of the imaging lens of example 1, respectively. Each aberration is based on the d-line (wavelength 587.6nm), but the aberrations with respect to the wavelengths 460.0nm and 615.0nm are also shown in the spherical aberration diagram, and particularly with respect to the wavelengths 460.0nm and 615.0nm are shown in the chromatic aberration of magnification diagram. In the astigmatism diagrams, this is indicated by a solid line for the radial direction and by a dashed line for the tangential direction. Fno of the spherical aberration diagram indicates the F value, and ω of the other aberration diagrams indicates the half field angle. The above-described method of expressing the aberration is the same as in fig. 11 to 18 described later.
As shown in fig. 10, the imaging lens of the present embodiment has a full field angle (2 ω) of 82.8 °, thereby ensuring a sufficiently wide field angle. In the imaging lenses of the other examples 2 to 9, as shown in fig. 11 to 18, the full field angle (2 ω) was in the range of 75.8 ° to 83.6 °, and a sufficiently wide field angle was achieved.
< example 2>
Fig. 2 shows the arrangement of lens groups in the image pickup lens of embodiment 2. The imaging lens of embodiment 2 is configured substantially similarly to the imaging lens of embodiment 1 described above, but differs in two points, that the 2 nd lens L2 is configured by a positive meniscus lens with the convex surface facing the object side, and the 6 th lens L6 is configured by a biconcave lens.
Since the above-described differences from example 1 also exist in examples 3 to 6 to be described later, the description of examples 3 to 6 will not be repeated.
Table 3 shows basic lens data of the imaging lens of example 2. Further, aspherical surface data of the image pickup lens of the present embodiment is shown in table 4. Further, (a) to (D) of fig. 11 show aberration diagrams of the imaging lens of example 2.
[ TABLE 3 ]
Example 2 basic lens data
*: aspherical surface
f＝18.851FNo.＝2.06
[ TABLE 4 ]
Example 2 aspherical data
< example 3>
Fig. 3 shows a lens group arrangement of an image pickup lens of example 3.
Table 5 shows basic lens data of the imaging lens of example 3. Further, aspherical surface data of the image pickup lens of the present embodiment is shown in table 6. Fig. 12(a) to (D) show aberration diagrams of the imaging lens of example 3.
[ TABLE 5 ]
Example 3 basic lens data
*: aspherical surface
f＝18.856FNo.＝2.07
[ TABLE 6 ]
Example 3 aspherical data
< example 4>
Fig. 4 shows a lens group arrangement of an image pickup lens of example 4.
Table 7 shows basic lens data of the imaging lens of example 4. Further, aspherical surface data of the image pickup lens of the present embodiment is shown in table 8. Further, (a) to (D) of fig. 13 show aberration diagrams of the imaging lens of example 4.
[ TABLE 7 ]
Example 4 basic lens data
*: aspherical surface
f＝18.854FNo.＝2.09
[ TABLE 8 ]
Example 4 aspherical data
< example 5>
Fig. 5 shows the arrangement of lens groups of the image pickup lens of example 5.
Table 9 shows basic lens data of the imaging lens of example 5. Further, aspherical surface data of the image pickup lens of the present embodiment is shown in table 10. Further, (a) to (D) of fig. 14 show aberration diagrams of the imaging lens of example 5.
[ TABLE 9 ]
Example 5 basic lens data
*: aspherical surface
f＝18.844FNo.＝2.06
[ TABLE 10 ]
Example 5 aspherical data
< example 6>
Fig. 6 shows the arrangement of lens groups of the imaging lens of example 6. The basic shapes of the 1 st lens L1 to the 8 th lens L8 of this embodiment are the same as those of the imaging lens of embodiment 1 described above.
Table 11 shows basic lens data of the imaging lens of example 6. Further, aspherical surface data of the image pickup lens of the present embodiment is shown in table 12. Further, (a) to (D) of fig. 15 show aberration diagrams of the imaging lens of example 6.
[ TABLE 11 ]
Example 6 basic lens data
*: aspherical surface
f＝18.176FNo.＝2.06
[ TABLE 12 ]
Example 6 aspherical data
< example 7>
Fig. 7 shows the arrangement of lens groups of an imaging lens in example 7. The imaging lens of embodiment 7 has substantially the same configuration as that of the imaging lens of embodiment 1 described above, but differs in that the 2 nd lens L2 is formed of a positive meniscus lens with the convex surface facing the object side.
Table 13 shows basic lens data of the imaging lens of example 7. Further, aspherical surface data of the imaging lens of the present embodiment is shown in table 14. Fig. 16(a) to (D) show aberration diagrams of the imaging lens of example 7.
[ TABLE 13 ]
Example 7 basic lens data
*: aspherical surface
f＝18.865FNo.＝2.06
[ TABLE 14 ]
Example 7 aspherical data
< example 8>
Fig. 8 shows the arrangement of lens groups of an imaging lens of example 8. The imaging lens of embodiment 8 has substantially the same configuration as that of the imaging lens of embodiment 1 described above, but differs in that the 2 nd lens L2 is formed of a positive meniscus lens with the convex surface facing the object side.
Table 15 shows basic lens data of the imaging lens of example 8. Further, aspherical surface data of the image pickup lens of the present embodiment is shown in table 16. Further, (a) to (D) of fig. 17 show aberration diagrams of the imaging lens of example 8.
[ TABLE 15 ]
Example 8 basic lens data
*: aspherical surface
f＝19.155FNo.＝2.06
[ TABLE 16 ]
Example 8 aspherical data
< example 9>
Fig. 9 shows the arrangement of lens groups of an imaging lens of example 9. The imaging lens of example 9 has substantially the same configuration as that of the imaging lens of example 1, but is different in two points that a cemented lens in which a biconvex lens 2a and a biconcave lens 2b are cemented is applied instead of the 2 nd lens L2 shown in fig. 1, and the 6 th lens L6 is formed of a biconcave lens. In this case, the cemented lens is a positive lens component of the group 12 lens G12.
Table 17 shows basic lens data of the imaging lens of example 9. Further, aspherical surface data of the image pickup lens of the present embodiment is shown in table 18. Fig. 18(a) to (D) show aberration diagrams of the imaging lens of example 9.
[ TABLE 17 ]
Example 9 basic lens data
*: aspherical surface
f＝18.856FNo.＝2.07
[ TABLE 18 ]
Example 9 aspherical data
[ TABLE 19 ]
Fig. 1 shows an example in which the optical member PP is disposed between the lens system and the image forming surface Sim, and instead of disposing a low-pass filter or various filters for cutting off a specific wavelength range, the various filters may be disposed between the lenses, or a coating layer having the same function as the various filters may be applied to the lens surface of any lens.
Next, an image pickup apparatus according to the present invention will be described. Fig. 19 shows a three-dimensional shape of a camera according to an embodiment of the present invention. The camera 10 shown here is a compact digital camera, and an imaging lens 12, which is a small wide-angle lens according to an embodiment of the present invention, is provided on and in a front surface of a camera body 11, a flash light emitting device 13 for emitting a flash light to an object is provided on the front surface of the camera body 11, a shutter button 15 and a power button 16 are provided on an upper surface of the camera body 11, and an imaging element 17 is provided in the camera body 11. The image pickup device 17 picks up an optical image formed by the small wide-angle lens 12 and converts the image into an electric signal, and is configured by, for example, a CCD, a CMOS, or the like.
As described above, the imaging lens 12 according to the embodiment of the present invention is sufficiently downsized, and therefore, even if the camera 10 is not of the retractable type, it is possible to form a compact camera both at the time of carrying and at the time of imaging. Alternatively, when the retractable camera is adopted, the camera can be made smaller and more portable than a conventional retractable camera. The camera 10 to which the imaging lens 12 of the present invention is applied can capture an image with high image quality and a wide angle of view.
Next, another embodiment of the imaging apparatus of the present invention will be described with reference to fig. 20A and 20B. Here, the camera 30 having a three-dimensional shape is a so-called mirrorless single-lens reflex type digital still camera to which the interchangeable lens 20 is detachably attached, and fig. 20A shows an appearance when the camera 30 is viewed from the front side, and fig. 20B shows an appearance when the camera 30 is viewed from the rear side.
The camera 30 includes a camera body 31, and a shutter button 32 and a power button 33 are provided on an upper surface thereof. Operation units 34 and 35 and a display unit 36 are provided on the back surface of the camera body 31. The display unit 36 displays an image to be captured and an image located within a field angle before the image capturing.
A photographing opening through which light from a subject to be photographed is incident is provided in the center portion of the front surface of the camera body 31, a mounting portion 37 is provided at a position corresponding to the photographing opening, and the interchangeable lens 20 is mounted on the camera body 31 through the mounting portion 37. The imaging lens of the present invention is housed in the barrel of the interchangeable lens 20.
Further, in the camera body 31 are provided: an image pickup device (not shown) such as a CCD that receives the subject image formed by the interchangeable lens 20 and outputs an image pickup signal corresponding to the subject image; a signal processing circuit for processing an image pickup signal outputted from the image pickup device to generate an image, and a recording medium for recording the generated image. In the camera 30, a still image is captured for one frame by pressing the shutter button 32, and image data obtained by the capturing is recorded in the recording medium.
By applying the imaging lens of the present invention to the interchangeable lens 20 used in such a mirrorless single-lens reflex camera 30, the camera 30 can be made sufficiently small in size in a lens-fitted state and can take an image with high image quality and a wide angle of view.
The present invention has been described above by way of the embodiments and examples, but the present invention is not limited to the embodiments and examples described above, and various modifications are possible. For example, the values of the curvature radius, the surface distance, the refractive index, the abbe number, the aspherical surface coefficient, and the like of each lens component are not limited to the values shown in the numerical examples described above, and may be other values.
Claims (19)
1. An imaging lens comprising a 1 st lens group having negative or positive refractive power, an aperture stop, and a 2 nd lens group having positive refractive power, which are arranged substantially in this order from an object side,
the 1 st lens group is substantially composed of three or less lenses as a whole, in which a 11 th lens group having negative refractive power and a 12 th lens group having positive refractive power are arranged in this order from the object side,
the 11 th lens group is composed of one 1 st lens, the 12 th lens group is composed of a positive lens component which is a single lens or a cemented lens arranged with an air gap from the 1 st lens,
the 2 nd lens group is substantially composed of a 21 st lens group having positive refractive power and a 22 nd lens group having negative refractive power arranged in this order from the object side,
the 21 st lens group has at least one positive lens and at least one negative lens,
the 22 nd lens group is substantially composed of a total of three lenses including at least one positive lens and at least one negative lens,
when the focal length of the entire lens system is f, the focal length of the 1 st lens group is f1, the axial distance between the image-side lens surface of the 1 st lens in the 1 st lens group and the lens surface of the positive lens component closest to the object side is d12, the axial distance from the lens surface of the 1 st lens group closest to the object side to the image forming surface in infinity object focusing is TL, and the maximum image height is Y, the following conditional expressions (1), (2), and (3) are satisfied,
-0.50＜f/f1＜0.20...(1)
0.08＜d12/f＜0.35...(2)
2.5＜TL/Y＜4.0...(3)。
2. the imaging lens according to claim 1,
satisfies at least one of the following conditional expressions (1 '), (2 ') and (3 '),
-0.45＜f/f1＜0.15...(1’)
0.10＜d12/f＜0.32...(2’)
2.7＜TL/Y＜3.8...(3’)。
3. the imaging lens according to claim 1 or 2,
satisfies the following conditional formula (1'),
-0.42＜f/f1＜0.10...(1”)。
4. the imaging lens according to claim 1 or 2,
the 22 nd lens group is composed of only a sub-lens group having negative refractive power and one positive lens, which are arranged in this order from the object side.
5. The imaging lens according to claim 1 or 2,
when an average value of refractive indexes with respect to a d-line of all the lenses arranged in the 22 Nd lens group is Nd22, the following conditional expression (4) is satisfied,
1.75＜Nd22...(4)。
6. the imaging lens according to claim 5,
satisfies the following conditional expression (4'),
1.78＜Nd22...(4’)。
7. the imaging lens according to claim 1 or 2,
in the 22 nd lens group, a lens having an aspherical surface on at least one surface is disposed.
8. The imaging lens according to claim 1 or 2,
in the 22 nd lens group, a negative lens is disposed in which a lens surface of a paraxial region on the object side is concave with respect to the object side and at least one surface is aspheric.
9. The imaging lens according to claim 1 or 2,
the 21 st lens group is composed of three lenses in total, namely, two lenses in which one lens is a positive lens and the other lens is a negative lens, and the two lenses are joined to each other, and one positive lens.
10. The imaging lens according to claim 1 or 2,
a positive lens having an aspherical surface on at least one surface is disposed in the 21 st lens group.
11. The imaging lens according to claim 1 or 2,
in an infinity object focusing state, when a distance on an optical axis from a lens surface closest to the object side of the 1 st lens group to a lens surface closest to the image side of the 2 nd lens group is Σ d and a distance on an optical axis from a lens surface closest to the object side of the 1 st lens group to an image forming surface is TL, the following conditional expression (5) is satisfied,
1.1＜TL/∑d＜1.5...(5)。
12. the imaging lens according to claim 11,
satisfies the following conditional expression (5'),
1.20＜TL/∑d＜1.45...(5’)。
13. the imaging lens according to claim 1 or 2,
when the focal length of the 1 st lens is f1n and the focal length of the entire system is f, the following conditional expression (6) is satisfied,
0.8＜|f1n|/f＜1.2...(6)。
14. the imaging lens of claim 13,
satisfies the following conditional expression (6'),
0.82＜|f1n|/f＜1.15...(6’)。
15. the imaging lens according to claim 1 or 2,
when the curvature radius of the image side lens surface of the 1 st lens is R12 and the curvature radius of the lens surface closest to the object side of the positive lens component is R21, the following conditional expression (7) is satisfied,
2.0＜(R21+R12)/(R21-R12)＜4.0...(7)。
16. the imaging lens of claim 15,
satisfies the following conditional expression (7'),
2.2＜(R21+R12)/(R21-R12)＜3.8...(7’)。
17. the imaging lens according to claim 1 or 2,
the 22 nd lens group is composed of three lenses of a negative lens, and a positive lens arranged in this order from the object side.
18. The imaging lens according to claim 1 or 2,
the 12 th lens group is composed of only one positive lens.
19. An image pickup apparatus is characterized in that,
an imaging lens according to any one of claims 1 to 18.
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2011-245309 | 2011-11-09 | ||
| JP2011245309 | 2011-11-09 | ||
| PCT/JP2012/007120 WO2013069262A1 (en) | 2011-11-09 | 2012-11-07 | Imaging lens and imaging device |
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| CN103917907B true CN103917907B (en) | 2016-05-18 |
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| JPWO2013069262A1 (en) | 2015-04-02 |
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